The Lives of Stars

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School

University of Toronto St. George

Department

Astronomy & Astrophysics

Course

AST201H1

Professor

Michael Reid

Semester

Winter

Description

AST201H-­‐
Stars
and
Galaxies
Professor
Michael
Reid
Lecture
Notes
Lecture
13:
Star
Formation
(continued)
Star
Formation
• From
a
molecular
cloud
fragment
to
a
spinning
disk
of
dust
and
gas
orbiting
a
protostar
à
a
protostar
surrounded
by
a
disk
and
a
bipolar
jets
• Light
reflected
from
the
far
side
of
the
disk
o Protostellar
jets
are
one
of
the
only
few
phenomena
in
the
universe
that
change
fast
enough
that
we
can
watch
them
doing
it
•
• Star
Formation
–
from
Protostar
o A
protostar
assembles
from
a
collapsing
cloud
fragment.
It
is
concealed
beneath
a
shroud
of
dusty
gas
o The
protostar
shrinks
and
heats
as
gravitational
potential
energy
as
converted
into
thermal
energy
o Surface
temperature
rises
when
radiation
becomes
the
dominant
mode
of
energy
flow
within
the
protostar
o The
fusion
rate
increase
until
it
balances
the
energy
radiated
from
the
star’s
surface
§ Fuse
hydrogen
into
helium
to
maintain
its
energy
o Protostars
start
off
being
big
and
bright
and
then
falls
on
to
the
main
sequence
(smaller
and
dimmer)
• It
is
very
hard
for
blue
giants
to
form.
Therefore,
there
are
more
red
dwarfs
than
blue
giants.
So
planets
can
take
time
to
form
(good
for
Cosmo
life)
• Radiation
blows
way
dust,
eventually
we
just
see
the
star
The
Lives
of
Star
• The
Death
of
the
stars
are
categorized
into
two
groups
by
mass
o Low
mass
stars
and
High
mass
stars
AST201H-­‐
Stars
and
Galaxies
Professor
Michael
Reid
Lecture
Notes
§ Low
mass
stars
and
high
mass
stars
have
very
similar
lives,
but
end
results
are
different
• End
results
for
low
mass
stars
are
white
dwarfs
and
planetary
nebula
• Low
Mass
Star’s
life
o When
the
stars
first
formed